U.S. patent application number 14/881415 was filed with the patent office on 2016-04-14 for method of regulating the speed at which a rotorcraft rotor is driven under icing conditions.
The applicant listed for this patent is AIRBUS HELICOPTERS. Invention is credited to Robert LESCHI, Andrea MUENZING.
Application Number | 20160101870 14/881415 |
Document ID | / |
Family ID | 52102719 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160101870 |
Kind Code |
A1 |
LESCHI; Robert ; et
al. |
April 14, 2016 |
METHOD OF REGULATING THE SPEED AT WHICH A ROTORCRAFT ROTOR IS
DRIVEN UNDER ICING CONDITIONS
Abstract
A method of regulating the NR speed at which the rotor of a
rotorcraft is driven in rotation. On detecting that the rotorcraft
is flying under icing conditions in a previously identified
critical temperature domain (Dct), the NR speed is either decreased
in the situation where the ambient outside air temperature (OAT)
lies in a low temperature icing range (Ptb) of the critical
temperature domain (Dct), or else it is increased in the situation
where the ambient outside air temperature (OAT) lies within a high
temperature icing range (Pth) of the critical temperature domain
(Dct).
Inventors: |
LESCHI; Robert; (Marseille,
FR) ; MUENZING; Andrea; (Salon De Provence,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AIRBUS HELICOPTERS |
Marignane |
|
FR |
|
|
Family ID: |
52102719 |
Appl. No.: |
14/881415 |
Filed: |
October 13, 2015 |
Current U.S.
Class: |
701/3 |
Current CPC
Class: |
B64C 13/04 20130101;
B64C 27/57 20130101; B64D 15/20 20130101; B64D 15/00 20130101; B64C
27/04 20130101; B64D 31/06 20130101 |
International
Class: |
B64D 15/20 20060101
B64D015/20; B64C 13/16 20060101 B64C013/16; B64C 13/04 20060101
B64C013/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2014 |
FR |
14 02311 |
Claims
1. A method of regulating the speed at which at least one rotor of
a rotorcraft is driven in rotation, referred to as the NR speed,
which NR speed varies over a predefined range of NR speed variation
under the control of at least one control unit generating a
setpoint, referred to as the NR setpoint, which NR setpoint is used
by a regulator unit to regulate the speed of operation of at least
one turboshaft engine supplying at least the mechanical power
needed for driving at least one rotor at an NR speed in compliance
with the NR setpoint, wherein the method comprises the following
operations: detecting that the rotorcraft is flying under icing
conditions; using the on-board instrumentation of the rotorcraft to
detect the ambient outside air temperature surrounding the
rotorcraft and to detect that the rotorcraft is flying in an
ambient outside environment at a temperature lying in a predefined
range of values, referred to as the critical temperature domain
(Dct), as identified between a predetermined high temperature (Th)
and a predetermined low temperature (Tb); and then after detecting
that the rotorcraft is flying in an ambient outside environment of
temperature (OAT) lying within the critical temperature domain
(Dct), and taking into consideration the low and high icing
temperature ranges (Ptb and Pth) respectively that extend on either
side of a temperature lying within the critical temperature domain
(Dct) between the high and low temperatures (Tb and Th), and
referred to as the middle temperature (Tm), the control unit
applies a relationship for calculating an NR setpoint, referred to
as the relationship (Lg) for calculating NR under icing conditions,
as follows: decreasing the NR speed in the situation where the
ambient outside air temperature (OAT) lies in the low temperature
icing range (Ptb) of the critical temperature domain (Dct); and
increasing the NR speed in the situation where the ambient outside
air temperature (OAT) lies in the high temperature icing range
(Pth) of the critical temperature domain (Dct).
2. A method according to claim 1, wherein the method comprises the
following operations: detecting that the rotorcraft is flying in
icing conditions, including at least one operation of the on-board
instrumentation of the rotorcraft measuring the ambient outside air
temperature (OAT) surrounding the rotorcraft; identifying that the
rotorcraft is flying at an ambient outside air temperature (OAT)
lying either in one or the other of the low and high temperature
icing ranges (Ptb and Pth) respectively of the critical temperature
domain (Dct), by comparing the ambient outside air temperature
(OAT) with the temperatures (Th, Tm, Tb) marking the boundaries of
each of the high and low temperature icing ranges (Pth and Ptb);
and identifying the current NR setpoint value generated by the
control unit and then: in the situation where the ambient outside
air temperature (OAT) lies outside the critical temperature domain
(Dct), the control unit continuing to generate the current NR
setpoint; in the situation where the ambient outside air
temperature (OAT) lies within the high temperature range (Pth), the
control unit increasing the value of the current NR setpoint within
the range of NR speed variation; and in the situation where the
ambient outside air temperature (OAT) lies in the low temperature
icing range (Ptb), the control unit decreasing the value of the
current NR setpoint within the range of NR speed variation.
3. A method according to claim 1, wherein the alternative
operations of increasing or conversely decreasing the NR speed
under icing conditions are performed by applying to the respective
NR setpoints values that are equal to the values marking the
boundaries of the range of NR speed variation.
4. A method according to claim 1, wherein the alternative
operations of increasing or conversely decreasing the NR speed
under icing conditions are performed by applying respective NR
setpoints having values that vary depending on the variation of the
ambient outside air temperature (OAT) within the high or low
temperature icing range (Pth, Ptb) under consideration.
5. A method according to claim 4, wherein the value of the NR
setpoints are varied depending on variation in the ambient outside
air temperature (OAT) by taking account of predefined sub-ranges of
temperature variation.
6. A method according to claim 1, wherein the relationship (Lg) for
NR calculation under icing conditions is applied while giving
priority to the execution of at least any one other calculation
relationship (L1, . . . , Ln) for causing a variation in the NR
speed by applying a predefined execution priority table for the
various predefined relationships (L1, . . . , Ln) for calculating
variation in the NR speed.
7. A method according to claim 1, wherein the relationship (Lg) for
calculating NR under icing conditions is incorporated in a
calculation rule that also incorporates at least any one other
relationship (L1, . . . , Ln) for calculation to vary the NR
speed.
8. A method according to claim 1, wherein the rotorcraft flying
under icing conditions is detected by a human pilot of the
rotorcraft, who then generates an order to execute the relationship
(Lg) for calculating NR under icing conditions.
9. A method according to claim 1, wherein the rotorcraft flying
under icing conditions is detected by at least one icing detector,
which then generates icing data leading to the relationship (Lg)
for calculating NR under icing conditions being executed.
10. A method according to claim 1, wherein the middle temperature
(Tm) is determined by the following calculation function:
OAT.sub.(critical)=-((y-1)/2yA).times.((2.pi..times.NR.times.R)/60).sup.2
in which calculation function: OAT.sub.(critical) is the middle
temperature (Tm); y is a constant having a value of 1.4; A has a
value of 287 J/kg.degree. K; NR is the current NR speed of the
rotor; and R is the radius of the rotor, the expression
((2.pi..times.NR.times.R)/60) identifying the speed at the tip of
the blade under consideration.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to French patent
application No. FR 14 02311 filed on Oct. 14, 2014, the disclosure
of which is incorporated in its entirety by reference herein.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention lies in the field of methods of
deicing outside surfaces of aircraft. More specifically, the
present invention relates to ways of deicing the blades of a
rotorcraft rotor.
[0004] (2) Description of Related Art
[0005] In the field of aviation, the problem arises of outside
surfaces of aircraft becoming iced. An aircraft may potentially fly
under icing conditions that lead to the formation of rime or even
solid ice on its outside surfaces, which is not desirable. Rime or
ice forming on the outside surfaces of an aircraft leads in
particular to the aircraft becoming heavier and also affects its
aerodynamic characteristics, thereby affecting its performance.
[0006] Icing conditions for the outside surfaces of an aircraft are
typically identified in application of various criteria including
in particular, for an aircraft or given structure, the overall
structure of the aircraft and the arrangement of its outside
surfaces under consideration, the aircraft's operating point within
its flight envelope, and atmospheric conditions.
[0007] The atmospheric conditions identifying icing conditions for
outside surfaces of an aircraft under consideration conventionally
vary depending on various meteorological parameters of values that
are identified during flight tests.
[0008] Among such meteorological parameters, account is taken in
particular of ambient temperature, of the concentration of water in
the ambient outside air, and of the mean volume diameter of the
water droplets contained in the ambient outside air.
[0009] For a rotorcraft in particular, it is observed more
particularly that the blades of the rotors of the aircraft lose the
greatest amount of performance when the aircraft is flying under
icing conditions in a determined ambient temperature range that is
referred to below as the "critical temperature domain".
[0010] The critical temperature domain is identified in particular
by temperature sensors, and it extends between a "low" temperature
and a "high" temperature. The concentration of liquid water in the
ambient outside air is commonly identified by icing detectors
and/or by specific probes, for example.
[0011] The mean volume diameter of droplets of water contained in
the ambient outside air is identified in particular by laser
droplet size probes, such as forward scattering spectrometer probes
(FFSP) or cloud droplet probes (CDP).
[0012] Other criteria based on the perception of the pilot may also
potentially be taken into account for identifying icing conditions
on outside surfaces of an aircraft, such as a variation in the
flying behavior of the aircraft, and in particular in its vibratory
behavior.
[0013] As a result of measurements taken during said test flights,
the pilot of a production aircraft having the same structure as the
aircraft used during said test flights can identify the icing
conditions to which the outside surfaces of the production aircraft
are subjected and can consequently adapt accordingly the way in
which the production aircraft is flown.
[0014] The pilot of the production aircraft can in particular
identify said icing conditions on the basis of values for
meteorological parameters as supplied by the on-board
instrumentation of the aircraft and/or by a weather station, and on
the basis of the pilot's own experience of the impact of
meteorological conditions on the behavior of the production
aircraft.
[0015] In addition, means for deicing the outside surfaces of an
aircraft are commonly operated as a result of icing conditions
being identified, either by the human pilot or else by ice
detectors identifying the presence of ice on the outside surfaces
of the aircraft, or indeed by instruments of the kind described in
Document GB 2 046 690 (Secretary of State for Defense). Such
instruments serve in particular to identify the presence of ice on
the blades of a rotorcraft rotor by comparing the real driving
torque delivered to the rotor with a predetermined driving torque
corresponding to operation under normal meteorological conditions,
i.e. in the absence of icing. By way of example, the predetermined
driving torque may be calculated in particular as a function of the
collective pitch (angle) of the blades of the rotorcraft rotor.
[0016] In this context, and more particularly concerning rotorcraft
flying under icing conditions, the formation of rime or ice on the
blades of a rotorcraft rotor affects the performance of the
rotor.
[0017] The formation of rime or ice on the blades of a rotorcraft
rotor is particularly harmful for the main rotor of a rotorcraft
that serves essentially to provide the rotorcraft with lift, and
possibly also with propulsion and/or guidance in flight in the
specific example of a helicopter.
[0018] When a rotorcraft is flying under icing conditions, any rime
or ice picked up on the blades of the rotor(s) of the rotorcraft
greatly decreases rotor performance. Such a loss of rotor
performance is induced in particular by a rapid increase in the
drag of the blades because of the deposition of rime or ice
changing their aerodynamic profile.
[0019] Furthermore, the rotors of a rotorcraft are conventionally
driven in rotation by a power plant of the rotorcraft that includes
at least one fuel-burning engine, in particular a turboshaft
engine.
[0020] A control unit generates a setpoint for the speed at which
each rotor, and in particular the main rotor, should be driven,
which setpoint is referred to as the NR setpoint. The NR setpoint
is transmitted to a regulator unit that regulates the speed of
operation of the engine(s) in order to drive the rotor(s), and in
particular the main rotor, at a speed referred to as the NR speed,
that complies with the NR setpoint.
[0021] Proposals have also been made concerning a main rotor of a
rotorcraft to cause the value of the NR setpoint to vary over a
range of values extending by way of example approximately from 92%
to 107% of the nominal speed of rotation at which the main rotor is
to be driven. Variation in the value of the NR setpoint is
controlled by the control unit in application of various criteria
for achieving specific results, such as a reduction in the noise
generated by the main rotor during a stage of approaching a landing
point, or increasing the performance of the rotorcraft when flying
in various specific stages of flight.
[0022] In this context, reference may be made for example to the
following Documents: FR 3 000 465 (Airbus Helicopter); US
2007/118254 (G. W. Barnes et al.); and WO 2010/143051 (Agusta S P A
et al.), which disclose various ways of controlling such variation
in the NR speed of a rotorcraft main rotor.
[0023] In a field remote from the present invention and relating to
wind turbines for producing electricity, methods are known for
identifying icing conditions of the blades of a rotor of a turbine
as a function of meteorological conditions.
[0024] By way of example, reference may be made on this topic to
the following Documents: EP 1 936 186 (General Electric company);
US 2012/0226485 (A. Creagh et al.); and EP 2 626 557 (Siemens A
G).
[0025] More particularly with reference to Document EP 2 626 557,
proposals have also been made to limit the icing of the blades of a
wind turbine rotor by varying the speed of rotation of said rotor.
More particularly, information about the rate of heat loss from the
blades is collected and the speed of the rotor is controlled
depending on that information.
[0026] By way of example, the rate of heat loss from the blades is
determined on the basis of a simulation or of a physical model of
the blades while the rotor is exposed to a given ambient
temperature and for a given ambient wind characterized by its speed
relative to the ground.
[0027] Still with reference to EP 2 626 557, account may also be
taken of the speed of rotation of the wind turbine, the rate of
heat loss from the blades possibly increasing with a decrease in
ambient temperature, depending on the increase in wind speed and/or
depending on the increase in the speed of rotation of the turbine.
The speed of rotation of the turbine is controlled with reference
to the rate of heat loss from the blades, for example by adjusting
the electrical power generated by the turbine.
BRIEF SUMMARY OF THE INVENTION
[0028] In this context, the present invention provides a method of
regulating the drive speed of at least one rotor of a rotorcraft
when said rotorcraft is under icing conditions. Said at least one
rotor of the rotorcraft is in particular at least one main rotor
having a drive axis that is substantially vertical and providing
the rotorcraft essentially with lift, and possibly also with
propulsion and/or guidance in flight in the specific example of a
helicopter. Nevertheless, it should be understood that the method
of the present invention is potentially applicable to regulating
the rotary drive speed of at least one auxiliary rotor of a
rotorcraft and having an axis that is substantially horizontal.
[0029] Such an auxiliary rotor conventionally forms an anti-torque
device for stabilizing and/or guiding the rotorcraft in yaw,
typically being formed by a tail rotor carried at the end of a tail
boom of the rotorcraft, or indeed potentially being formed by a
propulsive propeller in the example of a high forward speed
helicopter.
[0030] The present invention seeks more particularly to provide
such a method for controlling the effects on the performance of
said at least one rotor as a result of possible icing of the blades
making up its rotary wing when the rotorcraft is under icing
conditions.
[0031] In this context, the method of the present invention is a
method of regulating the rotary drive speed of at least one said
rotor of an aircraft, referred to as the NR speed, particularly but
not exclusively a main rotor serving essentially to provide the
rotorcraft with lift.
[0032] Said NR speed varies over a predefined range of NR speed
variation under the control of at least one control unit that
generates a setpoint referred to as the NR setpoint. On the basis
of said NR setpoint, a regulator unit regulates the operating speed
of at least one turboshaft engine supplying at least the mechanical
power needed for driving said at least one rotor at an NR speed in
compliance with the NR setpoint.
[0033] In the present invention, the method comprises the
operations described below.
[0034] Firstly, it is detected when the rotorcraft is flying under
icing conditions. The temperature of the ambient outside air
surrounding the rotorcraft is measured by the on-board
instrumentation of the rotorcraft, such as for example by a
temperature sensor of the rotorcraft.
[0035] It is then detected whether the rotorcraft is flying in an
outside environment at an ambient temperature lying within a
predefined range of values referred to as the critical temperature
domain. Said critical temperature domain is identified in
particular as extending between a predetermined high temperature
and a predetermined low temperature.
[0036] As mentioned above, the critical temperature domain is
typically previously identified during test flights on board a test
rotorcraft of given structure. In the specific example of a
rotorcraft rotor, in particular a main rotor, the critical
temperature domain conventionally lies within a temperature range
extending, by way of example, from a high temperature of -7.degree.
C. (minus 7.degree. Celsius) to a low temperature of -18.degree. C.
(minus 18.degree. Celsius).
[0037] Furthermore, and as mentioned above, the rotorcraft flying
under icing conditions may potentially be identified by taking
account of at least one criterion for identifying that the
rotorcraft flying under icing conditions identifying a severe risk
of the blades of said at least one rotor icing.
[0038] Such criteria identifying a severe risk of icing of the
blades of the rotor comprise for example, in isolation or in
combination:
[0039] for a given fixed operating point in flight, variation in
the drive torque delivered to the rotor by said at least one
turboshaft engine, e.g. and by way of indication a variation of
about 5%;
[0040] a variation in the vibratory behavior of the rotorcraft, in
particular as identified by the human pilot of the rotorcraft and
possibly also as identified by the on-board instrumentation of the
rotorcraft detecting a sudden variation in the vibratory phenomena
of the rotorcraft;
[0041] the concentration of water in the ambient outside air, in
particular as identified by information supplied by at least one
icing detector and/or specific probes mounted on board the
rotorcraft, for example, and/or also;
[0042] the mean volume diameter of water droplets contained in the
ambient outside air, which may potentially be identified by a laser
droplet size probe, for example.
[0043] Secondly, consideration is given to low and high temperature
icing ranges extending on either side of a temperature within the
critical temperature domain and lying between said high and low
temperatures respectively, which temperature is referred to as the
middle temperature.
[0044] In accordance with the approach of the invention, said
critical temperature domain is split into two distinct end
temperature ranges respectively constituted by said low temperature
icing range and by said high temperature icing range.
[0045] On detecting that the rotorcraft is flying in an outside
environment at an ambient temperature lying in said critical
temperature domain, a relationship is applied by the control unit
for calculating an NR setpoint, which relationship is referred to
as the relationship for calculating NR under icing conditions, and
is applied in the following manners:
[0046] decreasing the NR speed in the situation where the ambient
outside air temperature lies in the low temperature icing range of
the critical temperature domain; and
[0047] increasing the NR speed in the situation where the ambient
outside air temperature lies in the high temperature icing range of
the critical temperature domain.
[0048] In accordance with the approach of the present invention, it
is found that kinetic energy being exchanged between the blades and
the flow of air including droplets of water striking the leading
edges of the blades leads to heating, at least of the blades.
[0049] In this context, when the rotorcraft is flying in the low
temperature icing range, the present invention proposes decreasing
the NR speed so as to decrease the surface temperature of the
blades of the rotor, thereby making it possible to obtain shapes
that are more aerodynamic for the ice that is picked up on the
blades by virtue of a thermodynamic balance at the surfaces of the
blades that is more suitable for forming ice of known type commonly
referred to as "rime ice".
[0050] In addition, still in accordance with the approach of the
present invention, it is also observed that the further the
temperature of the ambient outside air drops within the critical
temperature domain, the more the concentration of water in the
ambient outside air decreases. It is more particularly proposed by
the present invention to make use of a potential reduction in ice
being picked up on the blades of the rotor as a result of such a
decrease in the concentration of water in the ambient outside
air.
[0051] Furthermore, when the rotorcraft is flying in the high
temperature icing range, the NR speed is increased in order to
avoid rime and/or ice forming on the blades, by taking the
opportunity to heat the blades as a result of supercooled water
droplets contained in the ambient outside air striking against
their leading edges. Proposals are made more particularly by the
present invention to take advantage of such heating of the blades
in order to oppose the formation of rime and/or ice on the blades
when the aircraft is flying in said high temperature icing
range.
[0052] On this topic, it should be recalled that in application of
the law of conservation of energy, said heating of the blades can
be expressed as follows:
Ttot-Ts=V.sup.2/2.times.J.times.Cp
where:
[0053] Ttot is the absolute temperature in degrees kelvin;
[0054] Ts is the static temperature in degrees kelvin;
[0055] V is the speed of the air relative to a given blade of the
rotor;
[0056] J is the calorie joule conversion factor; and
[0057] Cp is the specific heat of air at constant pressure.
[0058] In other words, the heating of the blades of the rotor,
which is proportional to the speed of the air relative to a given
blade raised to the power 2, increases with increasing speed at
which the rotor is driven.
[0059] Finally, such provisions make it possible to limit the
increasing drag effects that might be produced on the blades by the
formation of rime and/or ice when the rotorcraft is flying under
icing conditions at an ambient outside air temperature lying in the
critical temperature domain. When the aircraft is flying at an
ambient outside air temperature lying in said low temperature icing
range, the ice that is picked up by the blades is produced in
shapes that are more aerodynamic. Furthermore, the formation of
rime and/or ice on the blades of the rotor is limited when the
aircraft is flying under icing conditions while the ambient outside
air temperature lies in said high temperature icing range.
[0060] For temperatures lower than the temperatures defining the
critical temperature domain, the blades are completely iced.
Nevertheless, the icing of the blades under such conditions takes
place with the ice that is picked up by the blades of the rotor
being shaped in a manner that is less penalizing on the performance
of the rotor.
[0061] Finally, it can be seen from the provisions and selections
proposed by the present invention that as a result of increasing or
decreasing variation in the NR speed depending on the temperature
icing range under consideration, the overall effects on the loss of
performance of the rotor when the aircraft is flying under icing
conditions are attenuated.
[0062] More particularly, the method of the present invention
comprises the following operations:
[0063] detecting, in particular by means of on-board
instrumentation and/or by the human pilot of the rotorcraft, that
the rotorcraft is flying under icing conditions. On detecting that
the rotorcraft is flying under icing conditions, then the
instrumentation on board the rotorcraft performs at least one
operation of measuring the ambient outside air temperature
surrounding the rotorcraft;
[0064] identifying that the rotorcraft is flying at an ambient
outside air temperature lying either in one or the other of the low
and high temperature icing ranges of the critical temperature
domain. Such an identification operation is performed in particular
by comparing the ambient outside air temperature with temperatures
marking the boundaries of each of the low and high temperature
icing ranges, respectively. As a reminder, the high temperature
icing range extends from the high temperature to the middle
temperature, and the low temperature icing range extends from the
middle temperature to the low temperature;
[0065] identifying the current NR setpoint value generated by the
control unit and then: [0066] in the situation where the ambient
outside air temperature lies outside the critical temperature
domain, the control unit continuing to generate the current NR
setpoint; [0067] in the situation where the ambient outside air
temperature lies within the high temperature range, the control
unit increasing the value of the current NR setpoint within the
range of NR speed variation; and [0068] in the situation where the
ambient outside air temperature lies in the low temperature icing
range, the control unit decreasing the value of the current NR
setpoint within the range of NR speed variation.
[0069] In one implementation, the alternative operations of
increasing or conversely decreasing the NR speed under icing
conditions are performed by applying to respective NR setpoints
values that are equal to the values marking the boundaries of said
range of NR speed variation.
[0070] It should naturally be understood that in order to decrease
the NR speed, the value of the NR setpoint that is generated
corresponds to the low value of said range of NR speed variation,
and by way of indication for a main rotor, is about 92% of the
nominal speed at which rotation should be driven.
[0071] Likewise, in order to increase the NR speed, the value of
the NR setpoint corresponds to the high value of said range of NR
speed variation, and by way of indication, for a main rotor, is
about 107% of said nominal speed at which rotation should be
driven.
[0072] In another implementation, the alternative operations of
increasing or conversely decreasing the NR speed under icing
conditions are performed by applying respective NR setpoints having
values that vary depending on the variation of the ambient outside
air temperature within the high or low temperature icing range
under consideration.
[0073] By way of example, in order to avoid sustained variation in
the value of the NR setpoint, the value of the NR setpoints are
varied depending on variation in the ambient outside air
temperature by taking account of predefined sub-ranges of
temperature variation, and by way of example the sub-ranges may be
from 1.degree. C. to 3.degree. C. wide.
[0074] Furthermore, it is preferable to restrict execution of said
operation of NR variation under icing conditions in the event where
a variation in the NR speed is applied on the basis of other
criteria, such as for example the criteria that are taken into
account in above-mentioned Document FR 3 000 465.
[0075] More particularly, in a preferred implementation, said
relationship for calculating NR under icing conditions is applied
under the condition of giving priority to executing at least any
one other relationship for calculating a variation in the NR
speed.
[0076] It should naturally be understood in this context that
priority for executing said at least any one other calculation
relationship is taken into account in particular for reasons of
ensuring that the rotorcraft flies safely.
[0077] Said condition on varying NR under icing conditions is
applied in application of a predefined execution priority table for
the various predefined relationships for calculating variation in
the NR speed.
[0078] It should be observed that relationship for calculating NR
under icing conditions may advantageously be incorporated in a
calculation rule that also incorporates at least any one other
relationship for calculation to vary the NR speed.
[0079] Such provisions are particularly advantageous when such a
calculation rule, e.g. as disclosed in Document FR 3 000 465, could
lead potentially to continuous variation in the NR speed on the
basis in variation in the value of at least one physicochemical
parameter of air, such as its density.
[0080] The NR setpoint that is then deduced may be corrected by
calculation relationships that are specific to varying the value of
various parameters taken into account for varying the NR speed.
[0081] The rotorcraft flying under icing conditions may potentially
be detected by a human pilot of the rotorcraft, in particular by
the pilot of the rotorcraft sensing a change in the flying behavior
of the rotorcraft, including in particular vibratory phenomena or
for example by the human pilot observing ice forming on the walls
and/or accessories on the outside of the rotorcraft, such as wipers
for cleaning the transparent walls of the rotorcraft or on any
external element that projects from the rotorcraft and/or on any
wall of the rotorcraft lying in the field of view of the human
pilot.
[0082] Thereafter, on making such a detection, the human pilot then
generates an order to execute the relationship for calculating NR
under icing conditions, e.g. by activating a specific control
button that may advantageously be incorporated in a member for
generating manual flight controls as a result of being moved by a
person.
[0083] On its own or in combination with the above provisions, it
is possible to detect that the rotorcraft is flying under icing
conditions by means of an icing detector that then generates icing
data causing the relationship for calculating NR under icing
conditions to be executed.
[0084] Said middle temperature of the critical temperature domain
may potentially be a value that subdivides the low and high
temperature icing ranges equally.
[0085] Nevertheless, it is preferable to determine the value of
said middle temperature by calculation depending on the structure
of the rotorcraft. More particularly, and by way of example, said
middle temperature separating the low and high temperature icing
ranges from each other within the critical temperature domain may
be determined by the following calculation function:
OAT.sub.(critical)=-((y-1)/2yA).times.((2.pi..times.NR.times.R)/60).sup.-
2
in which calculation function:
[0086] OAT.sub.(critical) is said middle temperature;
[0087] y is a constant having a value of 1.4 and relates to the
ratio of specific heats of air, such that JCp=yA/(y-1) at subsonic
speeds;
[0088] A has a value of 287 J/kg.degree. K is the perfect gas
constant for air;
[0089] NR is the current NR speed of rotation of the rotor
expressed in revolutions per minute; and
[0090] R is the radius of the rotor, where the expression
((2.pi..times.NR.times.R)/60) gives the speed of the tip of said
rotating blade under consideration in meters per second.
[0091] The control unit acts iteratively at a given frequency to
calculate the value of the NR setpoint as a function of values for
the ambient outside air temperature as supplied continuously or
sequentially by the on-board instrumentation of the rotorcraft.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0092] Embodiments of the present invention are described with
reference to the figures of the accompanying sheet, in which:
[0093] FIG. 1 is a diagram showing variations in the NR speed of a
rotorcraft rotor using a general approach of the method of the
present invention; and
[0094] FIG. 2 is a block diagram showing specific implementations
of the method of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0095] FIG. 1 is a graph plotting a curve illustrating variation in
the power P needed for driving a rotorcraft rotor as a function of
variation in the ambient outside air temperature OAT surrounding
the rotorcraft.
[0096] When the rotorcraft is flying under icing conditions, a
critical temperature domain Dct is typically identified in which
the rotor blades are subjected to a risk of icing. The critical
temperature domain Dct is a temperature range extending between a
high temperature Th and a low temperature Tb. The critical
temperature domain Dct, which varies depending on the structure of
the rotorcraft, may be identified in conventional manner during
test flights, or by calculation, and/or on the basis of the
experience of the pilot performing said test flight.
[0097] In the example shown, consideration is given to a critical
temperature domain Dct defined between a high temperature Th of
about minus 7.degree. C. and a low temperature Tb of about minus
18.degree. C. Typically, the critical temperature domain Dct
corresponds to a range of temperatures in the ambient outside air
surrounding the rotorcraft in which the losses of rotor performance
are the greatest.
[0098] In the approach of the present invention, the critical
temperature domain Dct is subdivided into two icing temperature
ranges, referred to respectively as the high temperature icing
range Pth and the low temperature icing range Ptb, which ranges lie
on either side of a temperature within the critical temperature
domain that is referred to as the middle temperature Tm.
[0099] In the example shown, said middle temperature Tm is about
minus 15.degree. C., being defined by calculation depending on the
nominal speed at which the rotor is driven and/or depending on the
arrangement of the rotor, and in particular depending on the
structure of the blades making up its rotary wing.
[0100] In this context, it is proposed to cause the speed at which
the rotor is driven, referred to as the NR speed, to vary while the
rotorcraft is flying in the critical temperature domain Dct. The
ways in which the NR speed is varied are different depending on the
flying conditions of the rotorcraft in the critical temperature
domain Dct.
[0101] More particularly, in the present invention, the NR speed is
increased when the rotorcraft is flying in the high temperature
icing range Pth and the NR speed is decreased when the rotorcraft
is flying in the low temperature icing range Ptb. Specifically,
when the rotorcraft is flying in the critical temperature domain
Dct, blade icing conditions vary depending on the particular icing
temperature range under consideration.
[0102] In the high temperature icing range Pth, the water contained
in the ambient outside air is supercooled. When the rotorcraft is
flying in the high temperature icing range Pth, it is proposed to
increase the NR speed in order to avoid icing of the blades by
taking advantage of the blades being heated as a result of the
impact of supercooled drops of water contained in the ambient
outside air striking their leading edges.
[0103] In the low temperature icing range Ptb, it is proposed to
reduce the NR speed in order to reduce the surface temperature of
the rotor blades.
[0104] These provisions enable ice to be formed on the blades, and
in particular on their leading edges, which ice is of aerodynamic
shape, thereby limiting the loss of rotor performance.
[0105] FIG. 2 shows the ways in which the NR speed of a rotor 1 of
a rotorcraft flying in the critical temperature domain Dct can be
varied in compliance with the provisions shown in FIG. 1.
[0106] The rotor 1 is driven in rotation by a power plant 2
including at least one fuel-burning engine, in particular a
turboshaft engine. The operating speed of the engines is put under
the control of a regulator unit 3.
[0107] Depending on setpoints 22, referred to as NR setpoints,
which are generated by a control unit 4, the regulator unit 3
generates control signals 5 for regulating the operating speed of
the engine(s) of the power plant 2, typically such as signals for
controlling the supply of fuel to the engine(s).
[0108] Conventionally, the pitch of the blades of the rotor, and in
particular of the main rotor, is varied collectively and/or
cyclically under the effect of flight control signals CVm or CVa as
generated by a pilot of the rotorcraft. More particularly, a human
pilot 11 conventionally has manual control members 6 that generate
manual flight control signals CVm on being moved by a person.
[0109] Furthermore, the rotorcraft may potentially be fitted with
an autopilot 7 that generates automatic flight control signals CVa
when it is in operation in at least one mode of operation for
stabilizing and/or guiding the flight of the rotorcraft.
[0110] Furthermore, the rotorcraft has on-board instrumentation 8
including in particular sensors and/or probes for identifying the
flight conditions of the rotorcraft, in particular with respect to
its outside environment. The on-board instrumentation 8 includes in
particular at least one temperature sensor 9 measuring the
temperature of the ambient outside air surrounding the rotorcraft
and/or one or more ice detectors 10.
[0111] In conventional manner, the on-board instrumentation 8
supplies data relating to the rotorcraft flying under icing
conditions 12, e.g. on the basis of icing data 13 supplied by said
at least one ice detector 10.
[0112] The fact that the rotorcraft is flying under icing
conditions 12 can also be identified by the human pilot 11 of the
rotorcraft, e.g. by visually observing ice forming on the outside
surfaces of the rotorcraft, or indeed, by way of example, by
sensing a significant change in the behavior of the rotorcraft,
such as in particular variation in its vibratory behavior. The
human pilot 11 of the rotorcraft can then generate an order 14 to
execute a change in the NR speed by activating a specific control
button 15 dedicated to this purpose.
[0113] Temperature data 17 relating to the ambient outside air
temperature OAT is transmitted by the temperature sensor 9 to a
first computer 16 that is preferably incorporated in the control
unit 4. In the event of the rotorcraft flying under icing
conditions 12, the first computer 16 uses the temperature data 17
to identify the flying conditions of the rotorcraft relative to the
critical temperature domain Dct.
[0114] More particularly, depending on the temperature data 17, the
first computer 16 identifies that the rotorcraft is flying in the
high temperature icing range Pth or in the low temperature icing
range Ptb.
[0115] Depending on the flying conditions of the rotorcraft in one
or the other of the high or low temperature icing ranges Pth or
Ptb, respectively, the first computer 16 identifies various flying
situations of the rotorcraft for which the control unit generates
respective specific NR setpoints 22.
[0116] The first computer 16 identifies the various flying
situations of the rotorcraft by comparing the temperature data 17
with each of the temperatures marking the boundaries of the icing
temperature ranges Pth and Ptb, specifically firstly the high
temperature Th and the middle temperature Tm for the high
temperature icing range Pth, and secondly the middle temperature Tm
and the low temperature Tb for the low temperature icing range
Ptb.
[0117] In this context, the first computer 16 identifies in
particular:
[0118] a first situation C1 in which the rotorcraft is flying in an
outside environment at a temperature OAT that lies outside the
critical temperature domain Dct;
[0119] a second situation C2 in which the rotorcraft is flying in
an outside environment with a temperature OAT lying in the high
temperature icing range Pth; and
[0120] a third situation C2 in which the rotorcraft is flying in an
outside environment with a temperature OAT lying in the low
temperature icing range Ptb.
[0121] The second computer 18 executes a calculation rule 19
incorporating at least one relationship for calculating the NR
setpoint, referred to as the relationship Lg for calculating NR
under icing conditions, which rule serves to determine the value of
the NR setpoint depending on the flying situation of the rotorcraft
as previously identified by the first computer 16.
[0122] Naturally, the first computer 16 and the second computer may
potentially be incorporated in a single calculation unit that is
preferably incorporated in the control unit 4. Nevertheless, in
analogous manner, the first computer 16, the second computer 18,
and indeed said calculation unit, could be incorporated in any of
the calculation means on board the rotorcraft.
[0123] It should be observed that in conventional manner in the
context of controlled variation of the NR speed, the NR speed is
caused to vary in a predefined range 20 for variation of the NR
speed between a minimum NR speed NRmin and a maximum NR speed NRmax
that are typically identified relative to a nominal speed of
rotation NRnom. By way of indication concerning a main rotor, the
minimum NR speed NRmin is about 92% of the nominal speed of
rotation NRnom, and the maximum NR speed NRmax is about 107% of the
nominal speed of rotation NRnom. It should naturally be understood
that the values given for the minimum NR speed NRmin and the
maximum NR speed NRmax are given by way of indication and may vary
depending on the capabilities of the rotorcraft, or indeed on
technological change.
[0124] The NR setpoint is calculated more particularly by applying
the relationship Lg for calculating NR under icing conditions in
the following manners:
[0125] in the C1 situation where the ambient outside air
temperature OAT lies outside the critical temperature domain Dct,
the control unit 4 continues to generate the current NR
setpoint;
[0126] in the C2 situation in which the ambient outside air
temperature OAT lies in the high temperature range Pth, the current
NR setpoint 22 is increased; and
[0127] in the C2 situation where the ambient outside air
temperature OAT lies in the low temperature icing range Ptb, the
value of the current NR setpoint 22 is reduced.
[0128] In application of the relationship for calculating NR under
icing conditions 12, the value of the NR setpoint potentially
varies in a variety of alternative ways, such as for example in the
following ways:
[0129] either by applying predefined values, such as for example
the maximum NR speed NRmax in the second rotorcraft flight
situation C2 and the minimum NR speed NRmin in the third rotorcraft
flight situation C3;
[0130] or else by varying the value of the NR setpoint 22 as a
function of variation in the ambient outside air temperature OAT
within the icing temperature range Pth or Ptb under consideration,
preferably as considered in sub-ranges of temperature variation,
e.g. sub-ranges of 2.degree. C.
[0131] Furthermore, consideration should be given to the fact that
the calculation rule 19 potentially incorporates a plurality of
relationships L1, . . . , Ln for calculating the NR setpoint 22
using various criteria, such as the following non-limiting
criteria:
[0132] a criterion relating to the forward speed or to the rate of
altitude change of the rotorcraft;
[0133] a criterion relating to the stage of flight of the
rotorcraft, such as a takeoff stage, a landing stage, or a stage in
which the rotorcraft is in cruising flight;
[0134] a criterion of reducing sound nuisance generated by the
rotorcraft; and/or
[0135] a criterion relating to the altitude of the rotorcraft
and/or to the height at which it is flying above the ground.
[0136] In this context, is desirable for the generation of the NR
setpoint 22 by applying at least one of the relationships L1, . . .
, Ln for calculating the NR setpoint 22 to be determined on the
basis of a priority classification so as to avoid potential
conflicts between the various relationships L1, . . . , Ln for
calculating the NR setpoint 22.
[0137] For this purpose, the second computer 18 supplies a
predefined table 21 giving priority for executing the various
calculation relationships L1, . . . , Ln that are incorporated in
the calculation rule 19. The table 21 identifies priorities for
execution and/or for taking into consideration the various
relationships L1, . . . , Ln for calculating the NR setpoint as a
function of various predefined selection criteria.
[0138] By way of indication, such selection criteria relate in
particular to taking account of the rotorcraft flying under
conditions that are safe, e.g. with respect to its current stage of
flight, weather conditions, the rotorcraft's own mechanical power
resources, the mission of its flight, and/or the possibility of the
rotorcraft flying in a hostile environment.
* * * * *